Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing my new design;

FIG. 2 is front view of a second embodiment of a display screen or portion thereof with a graphical user interface showing my new design; and,

FIG. 3 is a front view of a third embodiment of a display screen or portion thereof with a graphical user interface showing my new design.

The outermost broken lines in the drawings illustrate the border of the display screen or portion thereof and form no part of the claimed design. The remaining broken lines shown within the display screen or portion thereof, including broken lines within the graphs and charts and the broken line indicia, form no part of the claimed design. The stippling and cross-hatching in the drawings are intended to show distinct elements of the graphical user interface and form part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 